Compositions comprising hexaphenoxy disilyl benzene



COMPOSITIONS COMPRISING HEXAPHENOXY DISILYL BENZENE Herbert C. Kaufman,New Haven, Conn., assignor to John B. Pierce Foundation, New York, N.Y.,a corporation of New York No Drawing. Application October 16, 1956Serial No. 616,126 7 11 Claims. 01. 252-78) This invention relates to afluid medium adapted to be usecl 1n the transfer of heat (as alubricant, and as a hydraulic fluid. It relates in particular to liquidorganosilicon compounds.

The criteria for a heat transfer medium include low starting viscosity,which has a practical bearing on its value as a heat transfer medium;high boiling point, which enables the material to be used at the hightemperatures which are required for many of the present day industrialneeds; and thermal stability, which permits the use of the material overa long period of time and at elevated temperatures.

Liquid heat transfer media which have the desired combination ofproperties of chemical stability at high temperature and fluidity at lowtemperature have long been sought. The Johnson U.S. Patent No. 2,335,012discloses as a heat transfer medium mixtures of tetra arylorthosilicates. The Morgan et al. U.S. Patent No. 2,674,579 disclosesmixtures of certain phenyl aryloxy silanes prepared by the reaction ofphenyltrichlorosilane with an equimolecular mixture of phenol andcresol. All of these compounds however suffer the disadvantage of havinga high viscosity after prolonged heating at high temperature, probablycaused by decomposition and polymerization.

In my co-pending patent application Serial No. 569,265 which was filedMarch 5, 1956, now U.S. Patent No. 2,834,736, I describe and claim thecompound hexaphenoxy ortho, meta or para disilyl benzene having thefollowing structural formula:

and its use in the transferring of heat. This material has the rareproperty of decreasing in viscosity upon heating. However, it would bedesirable to have a material which has a lower initial viscosity thanthe hexaphenoxy disilyl benzene. Although certain high temperature heattransfer fluids having a low initial viscosity are known at the presenttime, such liquids increase rapidly in viscosity during use due topolymerization or other causes as heretofore indicated.

Accordingly, it is an object of the present invention to supply amaterial which has a low initial viscosity and meets the other criteriaof a heat transfer fluid so that it may be successfully used in heattransmission, as a lubricant and as a hydraulic fluid.

Other objects and advantages of the invention will appear from thefollowing description.

The product which fulfills the objects and provides the advantages ofthe invention is a mixture of hexaphenoxy disilyl benzene which isdescribed in my copending application Serial No. 569,265 referred tohere- 2,934,502 Patented Apr. 26, 1960 tofore, and a normally solid (Le.at 25 C.) organic silicic ester having the following formula(R'),,Si-(O--R') where R is an aryl group, or aralkyl group of theformula (CH ),,-R, R is hydrogen, aryl or aralkyl of the formula --(CH),,-R, n is l or 2, R" is an aryl group, at is 1 to 4, y is 0 to 3, andthe sum ofx and y is 4. Preferably, R, R and R are aryl groups in whichthe sole aromatic nucleus is the benzene ring. Some examples of Stillanother such compound is tetra cyclohexyl silicate. The inventionprovides mixtures which unexpectedly have a lower initial viscosity thanthe liquid hexaphenoxy disilyl benzene, by adding a solid to suchliquid. Moreover, in most instances, the mixtures retain thecharacteristic decrease in viscosity on heating of the hexaphenoxydisilyl benzene.

In order to preserve the fluidity of the mixture and preventcrystallization or solidification, at ordinary temperatures, the amountof hexaphenoxy disilyl benzene in the mixture is maintained at least 40mol percent based on the mixture thereof with the normally solid silicicester and in the case of some of the mixtures of the invention, somewhatlarger amounts of hexaphenoxy disilyl benzene may be required in orderto prevent crystallization. Still larger amounts of the hexaphenoxydisilyl benzene of course may be used, but in order to effect asignificant decrease in initial viscosity and also for economicalreasons it is preferred to add at least 10 mol percent of the normallysolid organic silicic ester to the mixture, i.e., to limit the amount ofhexaphenoxy disilyl benzene to not greater than mol percent. Themixtures of the invention may be prepared by either of two methodsdesignated herein as method A and method B."

According to method A, a physical mixture of the liquid hexaphenoxydisilyl benzene and the solid silicic ester is prepared and heated forabout twenty-four hours at a temperature above 300 C. A vacuum ispreferably applied to the mixture after this heating process whereby anylow boiling impurities will be removed.

The preferred method (B) of preparing the mixture is to react a mixtureof hexachloro disilyl benzene and the chlorosilane corresponding withthe particular organic silicic ester to be used, with a stoichiometricexcess amount of phenol or alcohol having the aryl or aralkyl group thatis to be introduced to the components of the mixture. This process maybe carried out by the method described in my co-pending applicationSerial No. 569,265. Hydrogen chloride is liberated, and the mixture isrefluxed and'then stripped of low boilers while it is heated undervacuum.

The following examples illustrate methods for preparing the mixtures ofthe invention and show the superiority of such mixtures over other knownheat transfer liquids.

EXAMPLE I 536 grams (5.7 mols) of phenol were melted and poured into around-bottomed flask equipped with a dry ice-cooled reflux condenserleading to a fume hood. The flask was also equipped with a paddle-typemotor driven stirrer and a dropping funnel fitted with a calciumchloride drying tube. 122 grams (0.5 mol) of 3 hexachloro disilylbenzene (a mixture of the meta and para isomers, a commerciallyavailable material) were melted at 45 C. and added to 85 grams (0.5 mol)of silicon tetrachloride at 30 C. The resulting mixture 4 -n measurementat 770 F. The results of the aging and viscosity tests are presented inthe following Table l. The superscripts appearing in the table refer tothe number of days of continuous heating at 700 F., while the was pouredinto the dropping funnel and thence added 5 base numbers are theviscosity measurements in centislowly to the well-stirred phenol. Anendothermic reacstokes.

Table 1 Test Molal Initial No. Ratio Compound or Mixture vsecgtgigsy,Viscosity at 25 0. after Heating at 700 F.

1 i(z sisi o g 22s 154 134 1363 137 150 314 256 1,000 2 i i as 52 47" 7498 3 igigggg- 5s 59 89" 234 510 1, 730" tion ensued with the liberationof hydrogen chloride. It will be noted from Table 1 that the hexaphenoxyAfter all the chorosilanes had been added, heat was disilyl benzene inTest 1 had a high initial viscosity but applied slowly to the bottom ofthe round-bottomed flask decreased in viscosity as t progressed duringthe test, so as not to lose any silicon tetrachloride, which boils atwhile the mixture of the invention as in Test 2 exhibited 57.6 C.Temperature was gradually increased to the not only the decrease inviscosity with time, but also refluxing temperature of 320 C. and wasmaintained the unexpected low initial viscosity. In Test 3 a known atthis level for twenty-four hours to insure the removal heat transferliquid had an initial low viscosity but rapid "of all of th hydrogen hloide. Th fl k a th increase in viscosity was found to occur upon heating.cooled and vacuum was applied, thereby to remove low EXAMPLE IV boilingmaterials such as excess phenol. The pressure was maintained at about0.5 of mercury and the head A mixture of phenyl triphenoxy silane(melting temperature at 195 C. during this stripping process. Point 480and hexaphenoxy disilyl benzene in the After stripping, the residue wascooled to 100 C. and mol ratio of 030 1 respectively. was P p y filteredthrough dry Celite, an inert diatomaceous silica Method described above-The viscosity the P filter-aid. The filtrate was a clear brown liquid.The hexaphenoxy disilyl benzene was 216 Centlstokes and product, whichwas an equimolecular mixture of hexathe mixture (which was cOmplatelyliquid at had phenoxy i i benzene and tetraphenoxy silane, had a aninitial viscosity of 161 cs. After heat treatment at viscosity at 77 F.measured by the Fenske method of 700 F for nine dayS T ViSCPSitY 0f themixtures Was 63.0 centistokes. Its boiling point was 815 F. The 121completely hquld mlxtures of these two i d was 93% The mixture Showed noSign f l. terials containing as much as mol percent of phenyl lizationafter having been maintained at 37 F. for three trlphenoxy silane may bePrepared without the formation months. Completely liquid mixtures oftetraphenoxy of any crystl11s in themixture upon Standing at silane andhexaphenoxy disilyl benzene containing as 40 .EXAMPLEV much as 60 molercent of the tetra henox silane ma be prepared with but the formationof any crystals oh mlxture of dlphenyl hi Sflane .(meltmg pomt standingat 7 1 C.) and hexaphenoxy disilyl benzene 1n the mol ra- EXAMPLE II noof 50 to 50 was prepared by Method A. The viscosity of the purehexaphenoxy disilyl benzene was 216 Method A for the preparation of themixtures of cs. and the mixture (which was completely liquid at theinvention was carried out by mixing 345 grams 25 C.) had an initialviscosity of 200 cs. After heat (0.5 mol) of hexaphenoxy disilyl benzeneand 200 grams treatment at 7 0 F. for nine days the viscosity of the(0.5 mol) of melted tetraphenoxy silane. The mixture mixture was 157 cs.was heated for twenty-four hours at 360 C. and was EXAMPLE VI thencooled and stripped of any low boiling impurities by heating it under avacuum of 0.5 mm. of mercury A miXhlre 0f triphenyl P Y silane (meltingPohlt absolute pressure and a pot temperature of 200 C. heXaphenoXydisilyl benzene in the mol The residue was cooled to about 100 C. andfiltered Ratio of to 0-77, respectively, Was P p -l y through dry Celiteas in Example I. The clear, brown- Method The Viscosity 0f the p y f y ld li id product h d a b ili pgint'of 315 F benzene before mixing was 216es. and the mixture d a viscosity at 77 F f 620 (which was completelyliquid at 25 C.) had a viscosity of 185 cs. EXAMPLE III EXAMPLE 11Comparison viscosity and aging tests Were Carried out A mixture oftetra-p-cresyl silicate (melting point 69 on hexaphenoxy disilyl benzene(a miXture f meta and C.) and hexaphenoxy disilyl benzene in the molratio P isomers p pa y the method 0f Example of 0.40 to 0.60,respectively, was prepared by Method In a 5040 mol ratio .mixture oftetraphenoxy A. The viscosity of the hexaphenoxy disilyl benzene 5113116and P Y (mp) 551134 benzene (Test before mixing was 216 es. and themixture (which was and a 60-40 mol rtlo mixwlfe of Phenyl triphenoxycompletely liquid at 25 9 C.) had an initial viscosity lane and PhenyltrlcreSOXy silane (Test The tests of 92.6 cs. After heat treatment at700 FQfor nine were f m were out by Placing Sample of days the viscosityof the mixture was 53.9 cs., and 52.2 each liquid in a cylindrical tubehaving a narrow neck cs. after 4 davs at 00 Completely li id i ending na 2 mm. internal diameter capillary tube. An tures (at 25 C) can be dcontaining to b ut irondsttrlp was placeld trim the llqllfld to simulateTlllldlltStlgal 70 50 mol percent f i lid con irons in ac ua ea rans ersystems. e u es were then placed in a fused nitrate-nitrtite salt bathEXAMPLE VIII maintained at 700 F. Samples of the liquid were A mixtureof tetra cyc ohexyl silicate (melting point taken periodically byremoving the tube from the bath, 90 C.) and hexaphenoxy disilyl benzene.in the mol .cooling it, and withdrawing a sample for a viscosity ratioof .15 to .85, respectivelygwas prepared by Method A. The viscosity ofthe hexaphenoxy disilyl benzene before mixing was 216 es. and themixture (which was completely liquid at 25 C.) had an initial viscosityof 178 cs. After heat treatment at 700 F. for three days the viscosityof the mixture was 178 cs. 5

7 EXAMPLE IX A mixture of tetra thymyl silicate (melting point 48 C.)and hexaphenoxy disilyl benzene (initial viscosity 216 cs. beforemixing) in the mol ratio of .40 to .60, respec- 10 tively, was preparedby Method A. The mixture (which was completely liquid at C.) had aninitial viscosity of 69.3 cs. After heat treatment at 700 F. forthirteen days the viscosity of the mixture was 120 cs. Completely liquidmixtures (at 25 C.) can be made containing up 15 to about 50 mol percentof this solid.

EXAMPLE X A mixture of triphenoxy silane (melting point 55 C.) andhexaphenoxy disilyl benzene (initial viscosity before mixing 216 cs.) inthe mol ratio of .50 to .50 was prepared by Method A. The mixture (whichwas completely liquid at 25 C.) had an initial viscosity of-66 cs.

After heating at 700 F. for thirteen days the viscosity of the mixturewas 62 cs. Completely liquid mixtures (at 25 C.) can be made containingmore than mol percent of this solid.

EXAMPLE XII A mixture of hexaphenoxy disilylethane (melting point 88 C.)and hexaphenoxy disilyl benzene (initial viscosity before mixing 216cs.) in the mol ratio of .15 to .85 was prepared by Method A. Themixture (which was completely liquid at 25 C.) had an initial viscosityof 185 cs. After heat treatment at 700 F. for three days the viscosityof the mixture was 180 cs. 7

Although specific embodiments of the invention have 50 been describedherein and in the foregoing examples, it is intended to cover within thescope of the appended claims all modifications and equivalents withinthespirit and teaching of the invention. For example, the new heattransfer liquids of the invention may be used advantageously in thetransmission of heat as a transport fluid, i.e., a fluid may becirculated through a boiler or other heating medium to the locationwhere heat is needed and then returned to the boiler for reheating,whether it be high-grade heat for chemical processing, or low-gradespace heat used, e.g., in heating homes or offices.

I claim:

1. A mixture that is completely liquid at ordinary temperatures and isadapted to beused as a hydraulic 5 fluid and in heat transmission,consisting essentially of a mixture of at least 40 mol percent ofhexaphenoxy disilyl benzene having the following formula and theremainder, at least 10 mol percent, of a normally solid material of theclass consisting of (1) compounds having the structural formula where Ris of the class consisting of aralkyl groups of the formula (CH ),,R"and aryl groups, R is of the class consisting of aralkyl groups of theformula aryl groups and hydrogen, n is 1 to 2, R is an aryl group, x is1 to 4, y is 0 to 3, and the sum of x and y is 4, (2) hexaphenoxydisilylethane, and (3) tetracyclohexyl orthosilicate.

2. A mixture as described in claim 1 wherein said normally solidmaterial has the structural formula i-( and the symbols have themeanings therein assigned.

3. A mixture as described in claim 1 wherein said normally solidmaterial is hexaphenoxy disilylethane in an amount not exceeding about15 mol percent of the mixture.

4. A mixture as described in claim 1 wherein said normally solidmaterial is tetra cyclohexyl orthosilicate in an amount not exceeding 15mol percent of the mixture.

5. A mixture as described in claim 2 wherein R, R and R" are aryl groupsin which the sole aromatic nucleus is the benzene ring.

6. A mixture as described in claim 5 wherein R and R are phenyl groups.

7. A mixture as described in claim 5 wherein x is 4, y is O and R is thecresyl group.

8. A mixture as described in claim 5 wherein x is 2, y is 2 and R and Rare phenyl groups.

9. A mixture as described in claim 6 wherein x is 4 'and y is zero.

10. A mixture as described in claim 6 wherein at is 2 and y is 2.

11. A mixture as described in claim 6 wherein x is 3 and y is 1.

References Cited in the file of this patent UNITED STATES PATENTS2,584,334 DaFano Feb. 5, 1952 2,624,721 Hatcher et a1. Jan. 6, 19532,674,579 Morgan et al. Apr. 6, 1954 2,713,064 Weyenberg July 12, 1955OTHER REFERENCES Organo-Metallic and Organo-Metalloid High-TemperatureLubricants and Related Materials, by H. Gilman, WADC Technical Report53-426, Part II, Wright Air Development Center U.S.A.F.,Wright-Patterson Air Force Base, Ohio, pp. 74-77 (April 1955).

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.2,934,,502

Herbert G, Kaufman April 26, 1960 It is hereby certified that errorappears in the printed specification of the above numbered patentrequiring correction and that the said Letters Patent should readascorrected below.

for "30 c," read 20 c. line 28,

line 67, strike out were carried",

0 F." read 77 F. g

Column 3, line 4 after "0.5" insert mm. --,3 first occurrence; column 4,line 1, for "770 line 35 for "mixtures" read mixture Signed and sealedthis 20th day of September 1960.

(SEAL) Attest:

KARL Ho AXLINE Attesting Officer ROBERT c. WATSON Commissioner ofPatents

1. A MIXTURE THAT IS COMPLETELY LIQUID AT ORDINARY TEMPERATURES AND ISADAPTED TO BE USED AS A HYDRAULIC FLUID AND IN HEAT TRANSMISSION,CONSISTING ESSENTIALLY OF A MIXTURE OF AT LEAST 40 MOL PERCENT OFHEXAPHENOXY DISILYL BENZENE HAVING THE FOLLOWING FORMULA